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Pharmacology Exam 5 > Thyroid Drugs > Flashcards

Thyroid Drugs Flashcards

1
Q

Which organ systems does thyroid hormone regulate processes in?

A

nearly every one.

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2
Q

Which systems in particular do disorders of thyroid function have profound effects on?

A

cardiovascular, nervous, and metabolic systems

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3
Q

What are the 5 steps involved in thyroid function?

A
  1. active uptake of iodide from blood into thyroid follicle cells
  2. peroxidase enzyme mediates incorporation of iodide into tyrosine residues of the thyroglobulin (TG) protein.
  3. The peroxidase mediates the coupling of iodinated tyrosines to form thyroxine (T4) and triiodothyronine (T3). there is extensive storage of T3 and T4 within the follicle cells
  4. a protease enzyme releases T4 and T3 from TG for secretion into the circulation
  5. the prohormone T4 is converted to the active hormone T3 by deiodination in the liver and kidney
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4
Q

Which enzyme mediates incorporation of iodide into TG and coupling of tyrosines to T4 and T3?

A

peroxidase

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5
Q

Which enzyme releases T4 and T3 into blood?

A

protease

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6
Q

What does hypothyroidism cause?

A

decreased basal metabolic rate, decreased growth

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7
Q

What does hyperthyroidism cause?

A

increased basal metabolic rate, increased B-adrenergic activity

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8
Q

Which drugs are used for hypothyroidism (2)?

A

L-Thyroxine (T4), Triiodothyronine (Liothyronine) (T3)

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9
Q

Which drugs are used for hyperthyroidism (5)?

A

131-I, PTU, methimazole, K iodide, Propranolol

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10
Q

How long is therapy needed for hypothyroidism?

A

long-term therapy

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11
Q

What is the drug of choice for hypothyroidism?

A

Levothyroxine

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12
Q

How are doses changed for hypothyroidism?

A

dose changes are made slowly until a steady state level is reached.

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13
Q

what are the limitations to dosing for hypothyroidism?

A

physiologic doses can mimic hyperthyroidism - cardiovascular effects, weight loss, osteoporosis

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14
Q

Which two drugs are used to treat hypothyroidism?

A

L-thyroxine (L4) and Liothyronine (T3)

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15
Q

Where is T4 converted to T3?

A

in the liver

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16
Q

Why is Levo-thyroxine (T4) the drug of choice (5)?

A

its long half-life, low cost, converstion to T3, easy to monitor in the serum, no immediate CV effects

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17
Q

What are some characteristics of Liothyronine (Triiodothyronine) (T3) (3)?

A

active hormone, more potent, immediate CV effects

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18
Q

What are 4 etiologies of hyperthyroidism?

A

Graves’ Disease - diffuse toxic goiter (90%), toxic nodular goiter, subacute thyroiditis, postpartum thyroiditis

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19
Q

What is the rationale behind hyperthyroidism treatment?

A

to destroy hyperactive cells or directly inhibit thyroid hormone synthesis/release

20
Q

Which drugs are used to treat hyperthyroidism?

A

Thioamide drugs, 131 I, K iodide

21
Q

What are the therapeutic goals of hyperthyroidism treatment (3)?

A

control symptoms of thyrotoxicosis, reach euthyroid state, decrease auto-antibody levels

22
Q

Which drugs work on step 1 (iodide transport into thyroid gland)?

A

iodides

23
Q

Which drugs work on step 2 (iodide into TG)?

A

iodides, thioamides

24
Q

Which drugs work on step 3 (proteolysis)?

A

iodides

25
Q

Which drugs work on step 4 (T4 to T3)?

A

Ipodate, PTU, B-blockers, corticosteroids

26
Q

What are the thioamide drugs?

A

Methimazole and Propylthiouracil (PTU)

27
Q

What is the mechanism of the thioamide drugs?

A

both drugs directly inhibit peroxidase enzyme (step 2) in T4/T3 biosynthesis

28
Q

What else does PTU do? What does this mean?

A

PTU also inhibits deiodination of T4 to T3 in the liver (step 4). Thus, blood levels of T3 decline more rapidly than T4.

29
Q

What are the effects of the thioamide drugs (methimazole and PTU)?

A

slow onset, 2-4 weeks to become euthyroid due to continued release of preformed T4 and T3

30
Q

What is the toxicity of the thioamide drugs (methimazole and PTU)?

A

both drugs are well tolerated; skin rash is sometimes seen

31
Q

What is a limitation of hyperthyroidism treatment?

A

high relapse in Graves’ Disease due to continued autoantibody presence/production.

32
Q

What does relapse in Graves’ Disease signify?

A

persistence of a greater or lesser concentration of TSH-R Ab in the blood

33
Q

What is permanent remission associated with?

A

TSH-R being no longer measurable

34
Q

What does delayed response relapse reflect?

A

a lower level of TSH-R Ab

35
Q

How does Radioactive Iodine (131 I) work vs. hyperthyroidism (3)?

A

active uptake exclusively into thyroid follicle cells; localized tissue destruction; safe

36
Q

What are some cautions with Radioactive iodine?

A

children and older people; should not be used in pregnancy

37
Q

What are complications with radioactive iodine?

A

few, except transient hyperthyroidism and permanent hypothyroidism

38
Q

What is the mechanism of action of Potassium iodide (KI) in the tx of hyperthyroidism?

A

mechanism is “paradoxical” inhibition of iodine uptake (step 1), peroxidase enzyme (step #2), and proteolytic release of T4/T3 (step 3) in the thyroid cell

39
Q

What makes KI unique?

A

it is the only agent to inhibit release

40
Q

What else does KI do to the thyroid gland?

A

decreases the size and vascularity of the thyroid gland

41
Q

What is the limitation of KI?

A

short term effect for one week only

42
Q

What is the mechanism of propranolol in the tx of hyperthyroidism (2)?

A

symptomatic control of excessive B-adrenergic action. also inhibits T4 to T3 conversion in the liver (step #4). other lol’s have slight effect

43
Q

What is Ipodate?

A

iodinated radiocontrast media

44
Q

What does Ipodate do (2)?

A

inhibits T4 deiodination (step #4). rapidly decreases T3 concentrations

45
Q

3 random other things that you don’t really need to know?

A

1) hay treatments for specific forms of hyperthyroidism
2) new directions = combo of agents for immediate and long-term effects and prednisone for exopthalmus
3) hay a lot of drugs that alter binding of T4 to TBG (increase or decrease binding)

46
Q

What are the drugs to know (8)?

A

Levo-thyroxine (T4), Liothyronine (triiodothyronine/T3), Radioactive iodine (131 I), Methimazole, Propylthiouracil, Potassium Iodide, Propranolol, Ipodate

Pharmacology Exam 5 (9 decks)

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